posixshmcontrol
—
Control POSIX shared memory segments
posixshmcontrol |
create [-m
mode] [path ...] |
posixshmcontrol |
rm [path ...] |
posixshmcontrol |
ls [-h ]
[-n ] [-j
jail] |
posixshmcontrol |
dump [path ...] |
posixshmcontrol |
stat [-h ]
[-n ] [path ...] |
posixshmcontrol |
truncate [-s
length] [path ...] |
The posixshmcontrol
command manipulates the named POSIX
shared memory segments. It allows inspecting existing segments, dumping their
metadata or contents, and unlinking them.
Unlinking removes the name from the system and, when the last
process unmaps the segment and closes file descriptor pointing to the
segment, frees underlying memory.
The number of hard links as displayed by the
stat
subcommand, is equal to the number of
references to the underlying VM object. It is almost always equal to the
number of mappings +1, except for transient references.
The following subcommands are provided:
create
- Create segments with the specified paths, if not exist. The
mode optional numerical argument specifies initial
access mode.
rm
- Unlink the paths specified.
ls
- List all linked named shared memory segments visible to the caller. For
each segment, the user and group owner, size, and path are displayed. The
-j
option limits the output to segments within the
specified jail name or id.
dump
- Output raw bytes values from the segment to standard output.
stat
- Print metadata for the specified path, in the format similar to the
stat(1)
utility.
truncate
- Change the length of the segments. Argument to the
-s
option specifies new length. The human-friendly
'k', 'm', 'g' suffixes can be used, see
expand_number(3).
If the option is not specified, assumed length is zero.
For some commands, the following options may be provided:
-h
- If specified, requests human-readable display of size, see
humanize_number(3).
-n
- Prevent translation of owner and group into symbolic names using
name-switch services, instead the raw numeric values are printed.
The posixshmcontrol
utility exits 0 on success,
and >0 if an error occurs.
- To show content of the shared memory segment with the path
/1, use the command
posixshmcontrol dump /1 | hexdump
-C
- To create a segment with the path /2 and then
enlarge it to 1M, use the sequence of commands
posixshmcontrol create
/2
posixshmcontrol truncate -s 1m
/2
The posixshmcontrol
command appeared in
FreeBSD 12.1.
The posixshmcontrol
command and this manual page were
written by Konstantin Belousov
<kib@freebsd.org> under
sponsorship from The FreeBSD Foundation.